(1) Field of the Invention
This invention relates to a pneumatic tire provided with an inner liner having a favorable rubber composition and structure, and more particularly to a heavy duty pneumatic tubeless radial tire for use in trucks, buses and the like.
(2) Description of the Prior Art
In heavy duty pneumatic tubeless radial tire of this type, the inner liner is attached to the inner surface of the tire achieve air-impermeability and generally consists of one or two layers. Particularly, the layer directly contacting with air at the inner surface of the tire is usually composed of a composition containing a polymer such as butyl polymer, halogenated butyl polymer or the like in order to prevent air-permeation and further to prevent the penetration of water when metal cords are particularly employed as a carcass cord.
However, the tires of this type have been recently employed in an application range wider than before in view of improved roads and economical merits. Namely, such tires have been used in a wide range extending from a high-temperature district such as desert district to an extremely cold district, so that unexpected problems have come into existence.
In general, components and materials developed by mainly examining countermeasures to heat build-up have been used in the tires. Therefore, even if an inner liner is applied to the inner surface of the tire, a rubber composition composed mainly of a polymer having good heat properties as well as air- and water-impermeabilities such as halogenated butyl polymer, particularly bromobutyl rubber (Br-IIR) has been selected as a material for the inner linear. But, it has been found that the conventional inner liner of this type produces cracks in an area directly contacting with air or the inner surface when the tire is used in the cold district. This crack grows toward the inside of the tire and eventually brings about the reduction of the internal pressure. Furthermore, the inner liner is extended up to the lower region of each of the bead portions in view of the prevention of air leakage and vulcanized together with the other rubber material such as a bead portion-reinforcing rubber layer directly contacting therewith, but this bead portion-reinforcing rubber layer is composed of a composition mainly containing natural rubber (NR), so that the separation failure is apt to be caused due to the reduction of adhesion betweeen the inner liner and the bead portion-reinforcing rubber layer.